improve

docs/index.html

@@ -34,4 +34,13 @@
     navigator.serviceWorker.register('sw.js')
   }
 </script>
+<!-- Global site tag (gtag.js) - Google Analytics -->
+<script async src="https://www.googletagmanager.com/gtag/js?id=UA-139996012-1"></script>
+<script>
+  window.dataLayer = window.dataLayer || [];
+  function gtag(){dataLayer.push(arguments);}
+  gtag('js', new Date());
+
+  gtag('config', 'UA-139996012-1');
+</script>
 </html>